The present invention relates to a method and an apparatus for folding a web. More particularly, this invention relates to a method and an apparatus for folding a web by use of a continuous twist belt.
Conventional methods of making a longitudinal fold in a continuous web material generally employ stationary folding devices, such as rails or folding boards, and active folding devices, such as folding belts, which move with the web in the direction of the web to be folded.
Stationary folding devices, such as rails, are generally used for folding relatively stiff webs having both continuous and/or discontinuous longitudinal edges, and for folding soft, flexible webs having usually only continuous longitudinal edges. Other stationary folding devices, such as folding boards, are generally used for folding soft, flexible webs having usually only continuous longitudinal edges.
Active folding devices, such as folding belts, are generally used for folding both relatively rigid and soft, flexible webs having both continuous or discontinuous longitudinal edges. However, conventional belt folding devices do not work consistently well in folding relatively narrow longitudinal folds in soft, flexible webs.
One type of a conventional folding belt system 10 is illustrated in FIGS. 1-5, wherein the longitudinal axis of rotation 14 of the folding belt 12 is not parallel, (i.e., angled) to the fold line 24 of the web 18. (The term xe2x80x9clongitudinal axis of rotationxe2x80x9d refers herein to an axis around which a folding belt rotates or twists during folding a web.) In one embodiment, as shown in FIG. 1, the web 18 is disposed to a conveyor belt 20 (or any suitable web-supporting device) and folded inward along the first longitudinal edge 22 of the web 18 creating the fold line 24 and the longitudinally folded flap 25 along the fold line 24. The fold line 24 is substantially parallel to the longitudinal centerline 26 of the conveyor belt 20 and the machine direction 17. (The term xe2x80x9clongitudinal centerlinexe2x80x9d refers herein to a centerline which is equidistant between the opposing longitudinal edges of a belt. The term xe2x80x9cmachine directionxe2x80x9d refers herein to the direction in which the materials being processed move.) The web 18 travels in the first or machine direction 17, and the folding belt 12 travels in the second direction 19, which is angled in relation to the machine direction 17. Further, the longitudinal axis of rotation 14 of the folding belt 12 generally coincides with the longitudinal centerline 16 of the folding belt 12. FIG. 2 illustrates an initial arrangement of the folding belt 12 at a zero rotation position of the folding belt 12 in relation to the conveyor belt 20 and the web material 18, wherein the folding belt 12 is generally coplanar with the conveyor belt 20. FIG. 3 illustrates an intermediate arrangement of the folding belt 12 between the zero rotation position of FIG. 2 and a 90-degree rotation position of FIG. 4. FIG. 5 illustrates a final arrangement of the folding belt 12 in providing the longitudinally folded flap 25 along the fold line 24. As seen in FIGS. 3-4, during rotation of the folding belt 12, the first longitudinal edge 28 of the folding belt 12 loses its contact with the web 18 when the first longitudinal edge 28 rotates around the longitudinal axis of rotation 14 of the folding belt 12, away from the web 18. Furthermore, during this rotation, the web-contacting surface 29 of the folding belt 12 also moves away from the web 18. This relative movement between the web-contacting surface 29 of the folding belt 12 and the web 18 may result in wrinkles in the folding flap 25 and/or in improper fold configurations of the folded flap 25, especially when folding relatively narrow folds in soft, flexible webs.
Another type of a belt folding device is disclosed in U.S. Pat. No. 5,762,597, issued on Jun. 9, 1998 to Valterio. This device employs a folding belt supported by an under-belt track which forces the belt to rotate around an axis which is generally parallel to the machine direction and, thus, to the longitudinal fold line. However, the drawback of this device may be excessive wear of the folding belt and deteriorating quality of the fold due to a drag between the belt and the under-belt track.
Still another type of a belt folding device is disclosed in U.S. Pat. No. 4,795,416 issued on Jan. 3, 1989 to Cogswell et al. The device employs several folding belts disposed consecutively along the web path to fold the web in consecutive stages, wherein each folding belt rotates a portion of a total rotation required for providing a complete fold in a web. The shortcoming of this device may be a gap separating the sequential folding belts, especially, when folding discontinuous longitudinal edges in soft, flexible materials. The discontinuous edges may be caught in the gap and cause jams and/or inconsistency in quality of the folds.
Given the foregoing, there exists a continuing need in the art to provide a folding device for folding relatively narrow longitudinal fold(s), especially discontinuous, relatively narrow longitudinal folds(s) in soft, flexible webs. Further, it would be desirable to provide a folding device having a folding belt without the use of an under-belt track. Such needs are satisfied by the belt folder of the present invention.
In accordance with one aspect of the present invention, a method is provided for making a longitudinal fold in a web moving in a machine direction. The method generally includes the following steps: (1) providing a web-supporting device having a web-contacting surface and first and second opposing longitudinal edges; (2) providing a simply-supported folding belt disposed adjacent to the first longitudinal edge of the web-supporting device, the simply-supported folding belt includes a first surface contacting the web, a first longitudinal edge and a second longitudinal edge opposed thereto, a width extending between the first and the second longitudinal edges, a longitudinal centerline, and a longitudinal axis of rotation which is generally parallel to the longitudinal centerline; (3) providing the web having a first and a second longitudinal edges opposed to each other, the web being superimposed onto the web-contacting surface of the web-supporting device such that the first longitudinal edge of the web extends laterally beyond the first longitudinal edge of the web-supporting device and at least partially onto the first surface of the simply-supported folding belt; and (4) folding the first longitudinal fold of the web by twisting the simply-supported folding belt around its longitudinal axis of rotation such that the first surface of the simply-supported folding belt rotates toward the first longitudinal edge of the web-supporting device to face at least partially the web-contacting surface of the web-supporting device, wherein the longitudinal axis of rotation of the simply-supported folding belt extends substantially parallel to a longitudinal fold line of the longitudinal fold of the web. Furthermore, the longitudinal axis of rotation of the simply-supported folding belt of the present invention may be offset a distance from the longitudinal centerline, wherein the offset distance is less than half of the width of the simply-supported folding belt or substantially equal to the half of the width of the simply-supported folding belt or greater than half of the width of the simply-supported folding belt.